Low Noise, High Throughput 24-Bit Sigma-Delta ADC

FEATURES

24-Bit Sigma-Delta ADC

16 Bits p-p Resolution at 800 Hz Output Rate

Programmable Output Rates up to 6.4 kHz

Programmable Gain Front End 60.0015% Nonlinearity

Buffered Differential Inputs Programmable

Filter Cutoffs FASTStep™* Mode for Channel

Sequencing Single Supply Operation

APPLICATIONS

Process Control

PLCs/DCS Industrial

Instrumentation

GENERAL DESCRIPTION

The AD7731 is a complete analog front-end for process control applications. The device has a proprietary programmable gain front end that allows it to accept a range of input signal ranges, including low level signals, directly from a transducer. The sigmadelta architecture of the part consists of an analog modulator and a low pass programmable digital filter, allowing adjustment of filter cutoff, output rate and settling time.

The part features three buffered differential programmable gain analog inputs (which can be configured as five pseudo-differential inputs), as well as a differential reference input. The part operates from a single +5 V supply and accepts seven unipolar analog input ranges: 0 to +20 mV, +40 mV, +80 mV, +160 mV, +320 mV, +640 mV and +1.28 V, and seven bipolar ranges: ±20 mV, ±40 mV, ±80 mV, ±160 mV, ±320 mV, ±640 mV and ±1.28 V. The peak-to-peak resolution achievable directly from the part is 16 bits at an 800 Hz output rate. The part can switch between channels with 1 ms settling time and maintain a performance level of 13 bits of peak-to-peak resolution.

The serial interface on the part can be configured for three-wire operation and is compatible with microcontrollers and digital signal processors. The AD7731 contains self-calibration and system calibration options and features an offset drift of less than 5 nV/°C and a gain drift of less than 2 ppm/°C.

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